The invention relates to a process and apparatus for mixing carbonized and regenerated catalyst. A field of the invention may be the field of fluid catalytic cracking (FCC).
FCC is a hydrocarbon conversion process accomplished by contacting hydrocarbons in a fluidized reaction zone with a catalyst composed of finely divided particulate material. The reaction in catalytic cracking, as opposed to hydrocracking, is carried out in the absence of substantial added hydrogen or the consumption of hydrogen. As the cracking reaction proceeds substantial amounts of highly carbonaceous material referred to as coke are deposited on the catalyst to provide coked or carbonized catalyst. This carbonized catalyst is often referred to as spent catalyst. However, this term may be misconstrued because the carbonized catalyst still has significant catalytic activity. Vaporous products are separated from carbonized catalyst in a reactor vessel. Carbonized catalyst may be subjected to stripping over an inert gas such as steam to strip entrained hydrocarbonaceous gases from the carbonized catalyst. A high temperature regeneration with oxygen within a regeneration zone operation burns coke from the carbonized catalyst which may have been stripped.
Although the carbonized catalyst carries coke deposits it may still have activity. U.S. Pat. No. 3,888,762 discloses mixing carbonized and regenerated catalyst for contact with the hydrocarbon feed. The regenerated catalyst may be in the range of 593° to 760° C. (1100° to 1400° F.) and the carbonized catalyst may be in the range of 482° to 621° C. (900° to 1150° F.). U.S. Pat. No. 5,597,537 discloses mixing the carbonized and regenerated catalyst in a blending vessel to allow the regenerated and carbonized catalyst to reach a temperature equilibrium before contacting the hydrocarbon feed. U.S. Pat. No. 7,935,314 B2 discloses baffles in the riser to obstruct upward catalyst flow to foster mixing. A mixed catalyst with more uniform temperature avoids hot spots that can generate nonselective cracking to reduce the value of the product hydrocarbons.
Improved apparatus and processes are sought in the mixing of carbonized and regenerated catalyst.